The rates at which nonsmokers get lung cancer have increased by up to 15 percent.

A study presented at the World Conference on Lung Center this year revealed that the rate of people who have never smoked getting lung cancer have more than doubled from 2008 to 2014.

According to MedPage Today, nonsmokers make up 13 percent of nonsmall-cell lung cancer (NSCLC) patients at the start of the study in 2008, which rose to 28 percent by November 2014. Interestingly, two-thirds of NSCLC participants who are never-smokers are women.

"As this group of patients do not have established risk factors, research into early detection—ideally, by noninvasive or molecular screening—is urgently required to identify early lung cancer in nonsmokers," said Dr. Eric Lim of London's Royal Brompton Hospital. "We found that the absolute numbers are increasing in real time. But I say that with a caveat: We are starting from a position where we know the diagnosis. We really don't know the true incidence in the undiagnosed population."

For the study, the researchers looked at data gathered from database treated at the Royal Brompton Hospital. In more than 2,000 patients who had lung cancer surgery from 2008 to 2014, more than 400 were people who have never smoked, of which 67 percent were women. Most of the never-smokers who have the disease were diagnosed with advanced stages of lung cancer. According to Medscape, the incidence of never-smokers developing lung cancer increased every year, starting with 13 percent in 2008 to 28 percent in 2014.

"When we think of lung cancer, we think of smoking, what we are seeing is an increase in the incidence of nonsmoking-related lung cancer," Dr. Lim said, according to the report by the website. "We have seen more than double the amount of patients coming to us."

In their study, Dr. Lim and his colleagues found that more than half (52 percent) of their participants exhibited no clear symptoms. Hemoptysis or blood coughing was seen in only 11 percent of patients; chest infection was seen in 18 percent of them, cough was seen in 34 percent and lung cancer imaging was observed in 36 percent.

The presented study did not reveal why the fatal trend is happening to non-smokers. Dr. Everett Vokes from the University of Chicago speculates that it may be caused by exposure to second-hand smoke, small particles in the air, radon and air pollution.

As for early detection, Dr. Lim explained that more research on detection and "noninvasive or molecular screening" can be used to determine early stage lung cancer in neversmokers since they don't have established risk factors.